Helicobacter pylori is the predominant colonizing prokaryote in the human gastric niche. H. pylori infection results in persistent chronic inflammation, and is a strong risk factor for the development of peptic ulceration and gastric adenocarcinoma. The development of adenocarcinoma is dependent upon a variety of factors, including host genetics, diet, and bacterial factors. One specific feature that contributes to bacterial pathogenesis is the H. pylori cag pathogenicity island (cag PAI), which encodes a type IV secretion system (T4SS) responsible for the delivery of the oncogenic protein CagA into gastric epithelial cells. The T4SS apparatus spans two bacterial membranes and includes an extracellular organelle referred to as the T4SS pilus. This organelle is proposed to be responsible for compromising the eukaryotic membrane and translocation of CagA. Although the T4SS has an important role in H. pylori pathogenesis and ultimately carcinogenesis, the mechanisms that regulate assembly of this complex molecular machine are largely obscure. This application proposes experiments that will elucidate the mechanisms by which the cag T4SS is regulated. Specifically, we hypothesize that assembly of the T4SS pilus is regulated by the availability of metals such as iron and zinc. We will utilize a combination of electron microscopy, quantitative RT-PCR, and molecular biology techniques to shed light upon the complex regulatory networks that govern the biogenesis of this important organelle. PUBLIC HEALTH RELEVANCE: Helicobacter pylori is a bacterium that colonizes the human stomach and contributes to gastric cancer and peptic ulcer disease. This research seeks to understand how this bacterium regulates the cag type IV secretion system, which translocates carcinogenic effectors into host cells. This knowledge may lead to new approaches for the prevention and treatment of stomach cancer and peptic ulcer disease.